Reflection

As mentioned at the start of this chapter, reflection is the feature of C# that enables you to obtain information about a type. The term reflection comes from the way the process works: A Type object mirrors the underlying type that it represents. To obtain information, you ask the Type object questions, and it returns (reflects) the information associated with the type back to you. Reflection is a powerful mechanism because it allows you to learn and use the capabilities of types that are known only at runtime.

Many of the classes that support reflection are part of the .NET Reflection API, which is in the System.Reflection namespace. Thus, you will normally include the following in programs that use reflection:

 using System.Reflection;

The Reflection Core: System.Type

System.Type is at the core of the reflection subsystem because it encapsulates a type. It contains many properties and methods that you will use to obtain information about a type at runtime. Type is derived from an abstract class called System.Reflection.MemberInfo.

MemberInfo defines the following read-only properties:

Type DeclaringType	Obtains the type of the class or interface in which the member is declared.
MemberTypes MemberType	Obtains the kind of the member. This value indicates if the member is a field, method, property, event, or constructor.
int MetadataToken	Obtains a value linked to a specific metadata. (Added by C# 2.0.)
Module Module	Obtains a Module object that represents the module (an executable file) in which the reflected type resides. (Added by C# 2.0.)
string Name	The name of the type.
Type ReflectedType	The type of the object being reflected.

Notice that the return type of MemberType is MemberTypes. MemberTypes is an enumeration that defines values that indicate the various member types. Among others, these include

• MemberTypes.Constructor

• MemberTypes.Method

• MemberTypes.Field

• MemberTypes.Event

• MemberTypes.Property

Thus, the type of a member can be determined by checking MemberType. For example, if MemberType equals MemberTypes.Method, then that member is a method.

MemberInfo includes two abstract methods: GetCustomAttributes( ) and IsDefined( ). These both relate to attributes. MemberInfo also includes a method called GetType( ), which returns the Type object associated with the invoking object.

To the methods and properties defined by MemberInfo, Type adds a great many of its own. For example, here are several commonly used methods defined by Type:

Method	Purpose
ConstructorInfo[ ] GetConstructors( )	Obtains a list of the constructors for the specified type.
EventInfo[ ] GetEvents( )	Obtains a list of events for the specified type.
FieldInfo[ ] GetFields( )	Obtains a list of the fields for the specified type.
Type[ ] GetGenericArguments( )	Obtains a list of the type arguments bound to a constructed generic type, or the type parameters if the specified type is not constructed. (Added by C# 2.0. See Chapter 18 for a discussion of generics.)
MemberInfo[ ] GetMembers( )	Obtains a list of the members for the specified type.
MethodInfo[ ] GetMethods( )	Obtains a list of methods for the specified type.
PropertyInfo[ ] GetProperties( )	Obtains a list of properties for the specified type.

Here are several commonly used, read-only properties defined by Type:

Property	Purpose
Assembly Assembly	Obtains the assembly for the specified type.
TypeAttributes Attributes	Obtains the attributes for the specified type.
Type BaseType	Obtains the immediate base type for the specified type.
string FullName	Obtains the complete name of the specified type.
bool IsAbstract	Is true if the specified type is abstract.
bool IsArray	Is true if the specified type is an array.
bool IsClass	Is true if the specified type is a class.
bool IsEnum	Is true if the specified type is an enumeration.
bool IsGenericParameter	Is true if the specified type is a generic type parameter. (Added by C# 2.0. See Chapter 18 for a discussion of generics.)
bool IsGenericTypeDefinition	Is true if the specified type is an unconstructed generic type. (Added by C# 2.0. See Chapter 18 for a discussion of generics.)
string Namespace	Contains the namespace for the specified type.